The present invention relates generally to ink jet printers including printheads and, more particularly, to an assembly and method for scrubbing and priming each such printhead during periodic maintenance procedures.
An ink jet printer of the so-called xe2x80x9cdrop-on-demandxe2x80x9d type has at least one printhead from which droplets of ink are directed towards a recording medium. Within the printhead, the ink may be contained in a plurality of channels and energy pulses are used to cause the droplets of ink to be expelled, as required, from orifices at the ends of the channels.
In a thermal ink jet printer, the energy pulses are usually produced by resistors, each located in a respective one of the channels, which are individually addressable by current pulses to heat and vaporize ink in the channels. As a vapor bubble grows in any one of the channels, ink bulges from the channel orifice or nozzle until the current pulse has ceased and the bubble begins to collapse. At that stage, the ink within the channel retracts and separates from the bulging ink which forms a droplet moving in a direction away from the channel and towards a recording medium. The channel is then refilled by capillary action, drawing ink from a supply container.
One particular example of a type of thermal ink jet printer is described in U.S. Pat. No. 4,638,337. That printer is of the carriage type and has a plurality of printheads, each with its own ink supply cartridge, mounted on a reciprocating carriage. The channel orifices or nozzles in each printhead are aligned perpendicular to the line of movement of the carriage and a swath of information is printed on the stationary recording medium as the carriage is moved in one direction. The recording medium is then stepped, perpendicular to the line of carriage movement, by a distance equal to the width of the printed swath and the carriage is then moved in the reverse direction to print another swath of information.
It has been recognized that there is a need to maintain the ink ejecting orifices of an ink jet printer, for example, by periodically cleaning the orifices when the printer is in use, and/or by capping the printhead when the printer is out of use or is idle for extended periods. The capping of the printhead is intended to prevent the ink in the printhead from drying out. There is also a need to prime a printhead before use, to ensure that the printhead channels are completely filled with ink and contain no contaminants or air bubbles. Maintenance and/or priming stations for the printheads of various types of ink jet printers are described in, for example, U.S. Pat. No. 4,863,717 and the removal of gas from the ink reservoir of a printhead during printing is described in U.S. Pat. No. 4,679,059. All of these patents are hereby incorporated by reference.
Air bubbles in different locations of the ink path that feeds the thermal ink jet printhead can range from harmless to very problematic.
Removing these bubbles can be very difficult and requires the removal of large amounts of ink in order to xe2x80x9cpullxe2x80x9d the air bubble out. The problem is that air bubbles are difficult to break up and pull through the small nozzles of the printhead.
In accordance with the present invention, there is provided a scrubbing and priming method and apparatus for scrubbing and priming the nozzle face of an ink jet printhead. The apparatus of the method includes a capping member for capping a nozzle face of an ink jet printhead. The capping member has a bottom wall and side walls defining a capping recess and a priming path into the capping recess. A nozzle face of an ink jet printhead being capped, the bottom wall and side walls of the capping member together define an enclosed gap within the capping recess that contains air. The apparatus of the method then includes pressure applying devices for alternatingly applying positive and negative pressure within the enclosed gap and to nozzles in the nozzle face of the ink jet printhead being capped. The positive and negative pressures effectively agitate and scrub the nozzles in the nozzle face of the ink jet printhead being capped, thereby facilitating easy and effective subsequent priming of the nozzles in the nozzle face of the ink jet printhead being capped.